fluorapatite

Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca₅(PO₄)₃F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. Along with hydroxylapatite, it is an important constituent of tooth enamel.